\begin{tikzpicture}[>=Stealth, scale=0.85]
    \clip (0.05, 0) rectangle (7.95, -5.95);
    \draw (0, 0) -- (8, 0);
    \fill [pattern = dots] (0, 0) rectangle (8, -6);

    \filldraw [fill=white] (2, -4.2) -- (6, -3.0) --  (6, -3.8) -- (2, -5.0) -- cycle;

    \filldraw [fill=white] (1.5, 0) rectangle (2.3, -6);
    \filldraw [fill=white] (5.8, 0) rectangle (6.6, -6);

    \fill [fill=white] (2, -4.2) -- (6, -3.0) --  (6, -3.8) -- (2, -5.0) -- cycle;

    \node at (2.0, -4.8) {$A$};
    \node at (6.1, -3.8) {$B$};
    \draw [dashed] (2.3, -4.95) -- (5.8, -4.95)
        node [pos=0.6, below, fill=white, inner sep=3pt] {$120$};
\end{tikzpicture}
